Method for making yarns, fibres and filaments

ABSTRACT

The invention concerns a method for making yarns, fibres and filaments based on polyamide, and yarns, fibres and filaments obtainable by said method. The invention concerns a method for making yarns, fibres and filaments based on a polyamide composition having a molecular structure for enhancing overall productivity of the spinning process, in particular by improving the capacity for drawing the yarns produced thereby providing, for example, for a single identical spinning speed a much higher yarn meterage produced per time unit after drawing. The invention consists in a method for making synthetic yarns, fibres and filaments based on polyamide, comprising the following steps: i) mixing in molten phase the following compounds A and B: compound A: a linear polyamide; compound B selected in the group comprising: star-shaped or H-shaped macromolecular chains including one or several cores and at least three polyamide branches or three polyamide segments bound to said core, obtained from amino acid monomers and/or lactams, and as the case may be linear polyamide macromolecular chains obtained from amino acid monomers and/or lactams the melt index in molten phase of the polyamide or of the polyamide composition measured in accordance with the ISO 1133 standard at 275° C. under 100 g load being higher than 20 g/10 min, and a multifunctional compound comprising at least three identical acid or amine functions; ii) spinning the mixture in molten phase; iii) and optionally drawing said resulting yarns, fibres or filaments.

[0001] The present invention relates to a process for manufacturing polyamide-based yarns, fibers and filaments, and also to the yarns, fibers and filaments that may be obtained by the process.

[0002] Polyarnide-based yarns, fibers and filaments are produced by melt-spinning a polyamide or a polyamide-based composition. Melt-spinning consists in extruding the polyamide or the composition through dies and in cooling at the die outlets. Articles intended for use in many fields are thus manufactured. Examples that may be mentioned include multifilament yarns for the textile industry, fibers intended to be processed by spinning, or for the manufacture of nonwoven articles, cables intended to be chopped to form short fibers that may be flocked, and monofilaments and multifilaments for specific applications, especially industrial applications.

[0003] The processes for manufacturing yarns, fibers and filaments can vary considerably, especially in the field of the spinning speed. Depending on the type of process, the products obtained have different properties.

[0004] Various families of processes for manufacturing yarns, fibers and filaments are thus known. Mention is made, for example, of POY (Partially Oriented Yarn) high-speed spinning (speed of greater than 3 500 m/min), ISD (Integrated Spinning- Drawing) also known as FOY (Fully Oriented Yarn), and HOY (Highly Oriented Yarn) (speed of greater than 5 500 m/min) processes. Mention is also made of LOY (Low Oriented Yarn) low-speed spinning processes (speed of less than 3 500 m/min). These processes, and more particularly the LOY process, comprise a drawing step for improving the mechanical properties of the said products. This drawing step is also carried out for the manufacture of monofilaments. Furthermore, depending on the applications, a drawing operation may be applied to all the types of yarns obtained by the processes described above. Thus, the yarns obtained by the POY processes are very often drawn either directly on leaving the spinning process (integrated drawing), or in a separate step comprising an uptake of the yarns.

[0005] These processes are well known to those skilled in the art. They differ from each other, for example, in the spinning speeds, the method of cooling at the die outlet, and in the drawing operations possibly performed. In addition, the products obtained may undergo various specific treatments such as texturizing, ratching, twisting and setting, for example.

[0006] The processes used, and the technical parameters of these processes, depend to a large extent on the properties of the polyamide or of the polyamide-based composition used. Thus, the spinning speeds, temperatures and pressures that it is possible to use are determined relative to the properties of the polymer or of the composition to be spun, such as, for example, the heat stability and the melt viscosity.

[0007] Continued studies are undertaken to improve the production efficiency of these processes, that is to say to produce the longest possible metreage of yarns per unit of time.

[0008] To improve the production efficiency of these spinning processes, especially by improving the spinning speed, it has been proposed especially to modify the rheological properties of the composition to be spun by adding modifiers to the said composition.

[0009] Thus, for the manufacture of pre-oriented yarns based on polyethylene terephthalate, document U.S. Pat. No. 5,962,131 describes the addition, in the melt, of an immiscible copolymer forming small inclusions in the base polymer.

[0010] For the manufacture of polyamide-based pre-oriented yarns, document FR 2 677 376 describes the addition of nanometer-sized mineral particles. The presence of these particles allows the spinning speeds to be increased. However, it is difficult to obtain a good dispersion of the particles, to the extent that the level of breaks during spinning may be large.

[0011] One object of the present invention is to propose a process for manufacturing yarns, fibers and filaments based on a polyamide composition having a molecular structure that makes it possible to improve the total production efficiency of the spinning process, especially by improving the drawability of the yarns produced, thus making it possible to have, for example, for an identical spinning speed, a much higher metreage of yarns per unit of time produced after spinning.

[0012] To this end, the invention proposes a process for manufacturing synthetic, polyamide-based yarns, fibers and filaments, comprising the following operations:

[0013] i) Blending, in the melt, at least one of the compounds A and B below:

[0014] compound A: a linear polyamide

[0015] compound B chosen from the group comprising:

[0016] a polyamide or a polyamide composition comprising:

[0017] starburst or H-shaped macromolecular chains comprising one or more cores and at least three polyamide branches or three polyamide segments linked to the said core, obtained from amino acid and/or lactam monomers,

[0018] where appropriate, linear polyamide macromolecular chains obtained from amino acid and/or lactam monomers,

[0019] the melt flow index of the polyamide or of the polyamide composition measured according to ISO standard 1133 at 275° C. under a 100 g charge being greater than 20 g/10 min, and

[0020] a multifunctional compound comprising at least three identical acid or amine functions,

[0021] ii) spinning the blend in the melt, and

[0022] iii) optionally drawing the said yarn(s), fiber(s) or filament(s) obtained.

[0023] There are many advantages associated with the invention, and these depend on the process specifically used. These advantages may be observed during the spinning operation and especially during a subsequent operation such as drawing. These advantages make it possible to improve the production efficiency of the process or the possibility of manufacturing special products such as yarns or fibers with a very low yarn count.

[0024] The term “spinning” means the operation consisting in extruding the material in melt form through dies and then in cooling it between the dies and at least one first point of entrainment. The expression “process for manufacturing yarns, fibers and filaments” means the combination of steps leading to yarns, fibers and filaments. The process especially comprises the spinning operation. It may comprise other operations carried out after the spinning operation, including a drawing step (in continuous mode or in repeat mode), making it possible to improve the mechanical properties of the spun products and to obtain, for example, a rupture modulus and a residual elongation at break that are compatible with the processes for using these products and the processes for treating them. Processes for treating the spun products that may be mentioned include relaxing, curling, texturing, heat-setting and dyeing treatments.

[0025] The process according to the invention comprises an operation of melt-blending at least two compounds, a compound A and a compound B. The two compounds are thermoplastic. The blend may be obtained by any means conventionally used for producing a blend of two thermoplastic compounds, for example a single-screw or twin-screw and/or a barrier-screw extrusion device. It is possible, for example, to add granules of compound B to compound A in melt form, or to mix together granules of compound A and of compound B and to melt the blend of granules. It is also possible to add other additives to the blend, such as pigments, delustring agents, dull-spinning agents, catalysts, heat and/or light stabilizers, antibacterial agents and antifungal agents. It may be, for example, a dull-spinning agent chosen, for example, from titanium dioxide or zinc sulphide particles.

[0026] The melt-blending may be followed by a solidification and a granulation. The solid blend is then remelted for the spinning operation. Advantageously, the melt-blending operation is directly followed by the spinning operation, without intermediate solidification and granulation.

[0027] The blend of compounds is melt-spun. This operation is performed by extrusion through dies, at a suitably selected temperature and pressure. All the known spinning devices may be used.

[0028] According to one characteristic of the invention, compound A is a linear polyamide or a composition based on a linear polyamide. As examples of polyamides that may be used, mention may be made of polyamides of the type obtained from lactams and/or from amino acids. Mention is made in particular of nylon-6, nylon-11 and nylon-12, and blends and copolymers based on these polyamides. The linear polyamides may be used for the blending operation in pure form, or in the form of a composition with, for example, one of the additives mentioned above.

[0029] According to one preferential characteristic of the invention, compound A is a linear polyamide, or a composition based on a linear polyamide obtained from a diacid monomer and a diamine monomer. Examples of diacid monomers that may be mentioned include adipic acid, which is the preferred acid, decanoic acid or sebacic acid, dodecanoic acid, and phthalic acids such as terephthalic acid and isophthalic acid. Diamine monomers that may be mentioned include hexamethylene-diamine, methylpentamethylenediamine, 4,4′-diaminodicyclohexylmethane, butanediamine and meta-xylylenediamine. The polyamides obtained from these monomers are especially nylon-6,6 (polyhexamethylenediamine adipate), nylon-4,6 and nylon-6, 12. The linear polyamides that are suitable for the invention are also copolyamides comprising at least 90 mol % of repeating units corresponding to the polyamides described above, the other repeating units possibly originating from diacid, diamine, amino acid or lactam monomers. Copolyamides that may especially be mentioned include nylon-6,6/6 containing less than 5 mol % of nylon-6 units. The polyamides that are suitable for the invention may also comprise a monofunctional monomer conventionally used in the production of these polymers, as a chain-limiter.

[0030] Compound B is, in a first embodiment of the invention, a polymer or a polymer composition comprising starburst or H-shaped macromolecular chains and, where appropriate, linear macromolecular chains. Polymers or polymer compositions comprising such starburst or H-shaped macromolecular chains are described, for example, in documents FR 2 743 077, FR 2 779 730, U.S. Pat. No. 5,959,069, EP 0 632 703, EP 0 682 057 and EP 0 832 149. These compounds are known to have an improved melt index when compared with linear polyamides. The melt index of compound B used in the context of the invention, measured according to ISO standard 1133 at 275° C. under a 100 g load, is greater than 20 g/10 min.

[0031] The starburst or H-shaped macromolecular chains are obtained by using a multifunctional compound containing at least three reactive functions, all the reactive functions being identical. This compound may be used as a comonomer in the presence of other monomers in a polymerization process. It may also be placed in contact with a polyamide during an extrusion operation.

[0032] The starburst or H-shaped macromolecular chains comprise a core and at least three polyamide branches. The branches are linked to the core via a covalent bond, by means of an amide group or group of another nature. The core is an organic or organometallic chemical compound, preferably a hydrocarbon-based compound optionally comprising hetero atoms and to which the branches are linked. Branches are polyamide chains. They may show branching, and this is especially the case for the H-shaped structures. The polyamide chains constituting the branches are preferably of the type obtained by polymerization of lactams or amino acids, for example of nylon-6 type.

[0033] Compound B optionally comprises, in addition to the starburst or H-shaped chains, linear polyamide macromolecular chains. The weight ratio between the amount of starburst or H-shaped chains in compound B and the sum of the amounts of starburst or H-shaped chains and of linear chains is between 0.1 and 1, limits included. It is preferably between 0.5 and 1.

[0034] According to a first embodiment of the process of the invention, compound B is a starburst polyamide, that is to say a polyamide comprising starburst macromolecular chains, obtained by copolymerization using a monomer blend comprising:

[0035] a) a multifunctional compound comprising at least three reactive functions chosen from amines, carboxylic acids and derivatives thereof, all the reactive functions being identical,

[0036] b) monomers of general formulae (IIa) and (IIb) below:

X—R₂—Y  (IIa)

[0037] or

[0038] c) optionally, monomers of general formula (III) below:

Z—R₃—Z  (III)

[0039] in which:

[0040] Z represents a function that is identical to that of the reactive functions of the multifunctional compound

[0041] R₂ and R₃, which may be identical or different, represent substituted or unsubstituted, aliphatic, cycloaliphatic or aromatic hydrocarbon-based radicals containing from 2 to 20 carbon atoms, and possibly comprising hetero atoms,

[0042] Y is a primary amine radical when X represents a carboxylic radical, or

[0043] Y is a carboxylic radical when X represents a primary amine radical.

[0044] Such production processes are described in documents FR 2 743 077 and FR 2 779 730.

[0045] In the case where a co-monomer c) is used, the polymerization (polycondensation) reaction is advantageously carried out until the thermodynamic equilibrium is reached.

[0046] The monomer blend can comprise other compounds, such as chain limiters, catalysts or additives.

[0047] This process leads to the formation of starburst macromolecular chains, and optionally linear macromolecular chains. The percentage PS in numerical terms of starburst macromolecular chains relative to the total number of chains is determined by the following formulae:

[0048] in the case where the multifunctional compound contains 4 reactive functions: ${P\quad S} = {\frac{{4T_{0}{X_{d}^{3}\left( {1 - X_{d}} \right)}} + {T_{0}X_{d}^{4}}}{\begin{matrix} {{N_{0}\left( {1 - X_{d}} \right)} - {2R_{0}X_{d}} - {4T_{0}X_{d}} +} \\ {{R_{0}\left\lbrack {1 - \left( {1 - X_{d}} \right)^{2}} \right\rbrack} + {T_{0}\left\lbrack {1 - \left( {1 - X_{d}} \right)^{4}} \right\rbrack}} \end{matrix}} \times 100}$ in  which: $X_{d} = {1 - \frac{\lbrack{COOH}\rbrack}{{2\quad R_{0}} + {4\quad T_{0}} + N_{0}}}$

[0049] if the reactive functions are acid functions $X_{d} = {1 - \frac{N_{0} - \lbrack{NH2}\rbrack}{{2R_{0}} + {4T_{0}} + N_{0}}}$

[0050] if the reactive functions are amine functions T₀ represents the number of moles of multifunctional compound N₀ represents the initial number of moles of monomer of formula (IIa) or (IIb) R_(R) ₀ represents the initial number of moles of monomer of formula (III)

[0051] in the case where the multifunctional compound contains 3 reactive functions: ${P\quad S} = {\frac{T_{0}X_{d}^{3}}{{N_{0}\left( {1 - X_{d}} \right)} - {R_{0}X_{d}} - {3T_{0}X_{d}} + {T_{0}\left\lbrack {1 - \left( {1 - X_{d}} \right)^{3}} \right\rbrack}} \times 100}$ in  which: $X_{d} = {1 - \frac{\lbrack{COOH}\rbrack}{{2\quad R_{0}} + {3\quad T_{0}} + N_{0}}}$

[0052] if the reactive functions are acid functions $X_{d} = {1 - \frac{N_{0} - \lbrack{NH2}\rbrack}{{2R_{0}} + {3T_{0}} + N_{0}}}$

[0053] if the reactive functions are amine functions T₀ represents the number of moles of multifunctional compound N₀ represents the initial number of moles of monomer of formula (IIa) or (IIb) R₀ represents the initial number of moles of monomer of formula (III)

[0054] According to a second embodiment of the process, compound B is an H-shaped polyamide, that is to say a polyamide comprising H-shaped macromolecular chains, obtained by copolymerization using a monomer blend comprising:

[0055] a) 1 to 50 μmol per gram of matrix of a multifunctional compound comprising at least three reactive functions chosen from amines, carboxylic acids and derivatives thereof, the reactive functions being identical,

[0056] b) lactams and/or amino acids

[0057] c) a difunctional compound chosen from dicarboxylic acids and diamines,

[0058] d) a multifunctional compound whose function is chosen from amines, carboxylic acids and derivatives thereof,

[0059] the functions of c) and d) being amines when the functions of a) are acids,

[0060] the functions of c) and d) being acids when the functions of a) are amines,

[0061] the ratio in equivalents between the functional groups of a) and

[0062] the sum of the functional groups of c) and d) being between 1.5 and 0.66, the ratio in equivalents between the functional groups of c) and the functional groups of d) being between 0.17 and 1.5.

[0063] Such a process and such polymers are described in document U.S. Pat. No. 5,959,069.

[0064] According to a third embodiment of the process, compound B is obtained by melt-blending, for example using an extrusion device, of a polyamide of the type obtained by polymerization of lactams and/or of amino acids, and of a multifunctional compound comprising at least three identical reactive functions chosen from amine and carboxylic acid functions. The polyamide is, for example, nylon-6.

[0065] Such production processes are described in documents EP 0 682 070 and EP 0 672 703.

[0066] According to another embodiment of the invention, compound B is a multifunctional compound such as those used as the core for the synthesis of the starburst polyamides and/or H-shaped polyamides described above and below. This compound is added directly to compound A in the melt in a manner similar to the processes for introducing the compounds B of starburst polyamide or H-shaped polyamide type.

[0067] The multifunctional compounds used may be chosen from compounds with an arborescent or dendritic structure. They may also be chosen from the compounds represented by formula (I):

R1A—z]_(m)  (I)

[0068] in which:

[0069] R₁ is a linear or cyclic, aromatic or aliphatic hydrocarbon-based radical containing at least two carbon atoms and possibly comprising hetero atoms,

[0070] A is a covalent bond or an aliphatic hydrocarbon-based radical containing from 1 to 6 carbon atoms,

[0071] Z represents a primary amine radical or a carboxylic group,

[0072] m is an integer between 3 and 8.

[0073] According to another preferred characteristic, the radical R₁ is either a cycloaliphatic radical such as a tetravalent cyclohexanonyl radical, or a 1,1,1 -triylpropane or 1,2,3-triylpropane radical.

[0074] As other radicals R₁ that are suitable for the invention, mention may be made, for example, of substituted or unsubstituted trivalent phenyl and cyclohexanyl radicals, tetravalent diaminopolymethylene radicals with a number of methylene groups advantageously of between 2 and 12, such as the radical derived from EDTA (ethylenediaminetetraacetic acid), octavalent cyclohexanonyl or cyclohexadinonyl radicals, and radicals derived from compounds obtained from the reaction of polyols such as glycol, pentaerythritol, sorbitol or mannitol, with acrylonitrile.

[0075] The radical A is preferably a methylenic or polymethylenic radical such as ethyl, propyl or butyl radicals, or a polyoxyalkylenic radical such as a polyoxyethylenic radical.

[0076] According to one preferred embodiment of the invention, the number m is greater than 3 and advantageously equal to 3 or 4.

[0077] The reactive function of the multifunctional compound represented by the symbol X—H is a function capable of forming an amide function.

[0078] Examples of polyfunctional compounds of formula I may be mentioned include 2,2,6,6-tetra(β-carboxyethyl)cyclohexanone, diaminopropane-N,N,N′,N′-tetraacetic acid of the following formula:

[0079] or compounds derived from the reaction of trimethylolpropane or of glycerol with propylene oxide and amination of the hydroxyl end groups. The latter compounds are sold under the trade name Jeffamines TX by the company Huntsman, and have the general formula:

[0080] in which:

[0081] R₁ represents a 1,1,1-triylpropane or a 1,2,3-triylpropane radical,

[0082] A represents a polyoxyethylenic radical.

[0083] Examples of multifunctional compounds that may be suitable are mentioned especially in document U.S. Pat. No. 5,346,984, in document U.S. Pat. No. 5,959,069, in document WO 96/35739 and in document EP 672 703. Mention is made more particularly of:

[0084] nitrilotrialkylamines, in particular nitrilotriethylamine, dialkylenetriamines, in particular diethylenetriamine, trialkylenetetramines and tetraalkylenepentamines, the alkylene preferably being ethylene or 4-aminoethyl-1,8-octanediamine. Mention is also made of the dendrimers of formula (II)

(R₂N—(CH₂)_(n))₂—N—(CH₂)_(x)—N—((CH₂)_(n)—NR₂)₂  (II)

[0085] in which

[0086] R is a hydrogen atom or a group —(CH₂)_(n)—NR¹ ₂ in which

[0087] R¹ is a hydrogen atom or a group —(CH₂)_(n)—NR² ₂ in which

[0088] R² is a hydrogen atom or a group —(CH₂)_(n)—NR³ ₂ in which

[0089] R³ is a hydrogen atom or a group —(CH₂)_(n)—NH₂,

[0090] n being an integer between 2 and 6

[0091] x being an integer between 2 and 14.

[0092] n is preferably an integer equal to 3 or 4, in particular 3, and x is preferably an integer between 2 and 6 (limits included), preferably equal to 2, 3 or 4 and in particular 2. Each radical R may be chosen independently of the others. The radical R is preferably a hydrogen atom or a group —(CH₂)_(N)—NH₂.

[0093] Mention is also made of multifunctional compounds containing 3 to 10 and preferably 3 or 4 carboxylic acid groups. Among these, the ones that are preferred are compounds containing an aromatic and/or heterocyclic ring, for example benzyl, naphthyl, anthracenyl, biphenyl and triphenyl radicals, or heterocycles, for instance pyridine, bipyridine, pyrrole, indole, furan, thiophene, purine, quinoline, phenanthrene, porphyrine, phthalocyanine and naphthalocyanine. 3,5,3′,5′-Biphenyltetracarboxylic acid, acids derived from phthalocyanine and from naphthalocyanine, 3,5,3′,5′-biphenyltetracarboxylic acid, 1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridinetricarboxylic acid, 3,5,3′,5′-bipyridyltetracarboxylic acid, 3,5,3′,5′-benzophenonetetracarboxylic acid and 1,3,6,8-acridinetetracarboxylic acid are most particularly preferred, and even more particularly trimesic acid and 1,2,4,5-benzenetetracarboxylic acid. Mention is also made of multifunctional compounds whose core is a heterocycle containing a point of symmetry, for instance 1,3,5-triazines, 1,4-diazines, melamine, compounds derived from 2,3,5,6-tetraethylpiperazine, 1,4-piperazines and tetrathiafulvalenes. Mention is made more particularly of 1,3,5-triazine-2,4,6-triaminocaproic acid (TTAC).

[0094] The weight proportion of compound B relative to the weight of compounds A and B in the blend is advantageously less than 30%, preferably less than 20% and even more preferably less than 15%. According to this characteristic, no account is taken of the possible presence of other additives.

[0095] The yarns, fibers and filaments obtained from the blend of compounds A and B comprise starburst or H-shaped polyamide macromolecular chains and linear polyamide chains. The weight proportion of the starburst or H-shaped macromolecular chains relative to the total weight of the starburst or H-shaped and linear macromolecular chains is preferably less than 25% and even more preferably less than 15%.

[0096] In a first embodiment, the process according to the invention can be used in the context of a high-speed spinning process, for example at speeds above 3 500 m/min, of POY, HOY or FEI type, for the manufacture of multifilament yarns, or in the LOY process for the manufacture of fibers.

[0097] The yarns obtained have, surprisingly, a drawability that is greater than that observed with the yarns obtained from linear polyamide conventionally used, such as nylon-6,6 for mechanical properties that are comparable and compatible with the use of these products in the various applications such as the textile industry. Specifically, the products obtained according to the process of the invention have a rupture modulus and a residual elongation at break equivalent to those shown by nylon-6,6 yarns.

[0098] This improved drawability thus makes it possible to improve production efficiency of the process for manufacturing yarns either by increasing the spinning speed or by increasing the draw ratio applied to the yarns obtained or by applying these two increases. In other words, the process of the invention makes it possible to manufacture yarns, fibers or monofilaments with application of a global draw ratio, the draw ratio applied to the spinning plus the draw ratio applied during the drawing step, that is higher than that which may be applied to linear polyamide yarns, for the same level of rupture modulus and elongation at break for the yarn thus obtained.

[0099] The process of the invention also makes it possible to produce, by melt-spinning and drawing, yarns with a very fine yarn count, for example of less than 0.8 dtex and preferably less than 0.6 dtex. Specifically, it is possible according to the process of the invention to produce yarns at the die outlet with a fine yarn count, in a manner similar to that obtained with a linear polyamide, and with a similar device. However, since it is possible to apply a higher draw ratio to the yarns obtained by the process of the invention, it is easy to understand that the final yarn count of the yarn according to the invention is markedly lower for equivalent mechanical properties. This possibility is especially very advantageous for the manufacture of fibers with a very small yarn count.

[0100] According to a second embodiment, the process according to the invention can be used in the context of a manufacture of yarns, fibers and filaments starting with a linear polyamide of high molecular mass. These polyamides are generally used to obtain improved mechanical properties and/or improved chemical resistance or heat resistance properties, for instance abrasion resistance. It is in particular adapted to the manufacture of fibers for felts for paper machines. The use of compound B makes it possible to spin at a lower temperature and/or at lower pressure compared with the conditions that would be necessary in the absence of the compound. It is thus possible either to obtain yarns that are more resistant to abrasion since the molecular mass of the polyamide is higher, or to obtain fibers whose properties are similar, with a less restrictive process. By way of specific embodiment, the linear polyamide is a nylon-6 whose relative viscosity, measured at 25° C. at a concentration of 0.01 g/ml in a 96% sulphuric acid solution, is greater than 3.5 and preferably greater than 3.8.

[0101] According to one specific embodiment, during the operation for blending compounds A and B, these compounds are introduced in dried form, preferably with a moisture content of less than 0.3%, and a compound capable of catalysing the polycondensation of the polyamide is added, preferably in a weight concentration of between 0.005% and 5%. This compound may be chosen from phosphorus compounds, for example phosphoric acid or tris(2,4-di-tert-butylphenyl) phosphite (sold by the company CIBA under the reference Irgafos 168, or as a blend with N,N-hexamethylenebis(3,5-di-tert-butyl-4-hydroxyhydrocinnamide) under the reference Irganox B 1171). This compound may be added in the form of powder or in the form of concentrate to a polyamide matrix (masterbatch). The blending of the various compounds is carried out in a single-screw or twin-screw extrusion device.

[0102] For the manufacture of fibers intended to be used in non-woven form in paper machine felts, the spinning is generally carried out at moderate speed, of less than 1 000 m/min, with a subsequent drawing operation.

[0103] Other details or advantages of the invention will emerge more clearly in the light of examples below, given purely as a guide.

[0104] The following compounds are used:

[0105] Compound A: nylon-6,6 with a viscosity index of 136 ml/g, measured at 25° C. at a concentration of 0.01 g/ml in a 90% formic acid solution, with a concentration of acid end functions (GTA) of 55 meq/g of polymer and a concentration of amine end functions (GTC) of 66 meq/g of polymer.

[0106] Compound B: starburst polyamide, obtained by copolymerization using caprolactam in the presence of 0.5 mol % of 2,2,6,6-tetra(carboxyethyl)cyclohexanone, according to a process described in document FR 2 743 077, comprising about 80% of starburst macromolecular chains and 20% of linear macromolecular chains, with a viscosity index of 98.2 ml/g measured according to the method described above and a GTA of 13.9 meq/g and a GTC of 165.3 meq/g, and a melt index in the melt, measured at 275° C. under 100 g, of 55 g/10 minutes. Compound C: nylon-6 with a relative viscosity, measured at 25° C. at a concentration of 0.01 g/ml in a 96% sulphuric acid solution, of about 3.8, sold by the company BASF under the reference B4000.

[0107] The elongation at break and breaking stress properties of the yarns are determined on an Erichsen tensile testing machine placed in an air-conditioned room at 50% RH and 23° C. after conditioning the yarns for 72 hours under these conditions. The initial length of the yarns is 50 mm and the running speed is 50 mm/min. These measurements are performed according to ISO standard 2062 or AFNOR standard 07-002.

EXAMPLES 1 TO 4

[0108] The compounds are melt-blended using a single-screw extrusion device and the melt is then spun, with a speed at the first point of call, also known as the spinning speed, of 4 200 m/min, so as to obtain a continuous yarn comprising 34 filaments with a total yarn count indicated in Table I below. The spinning conditions are collated in Table I below, the properties of the yarns obtained being collated in Table II. TABLE I Flow Die rate of temper- Spinning polymer Spinning Composition ature pressure in the speed Ex. (% by weight) (° C.) (bar) die g/min (m/min) 1c Compound A: 100% 276 230 1.23 4 200 2 Compound A: 90% 276 280 1.23 4 200 Compound B: 10% 3 Compound A: 90% 276 280 1.23 4 800 Compound B: 10% 4 Compound A: 90% 276 280 1.23 5 400 Compound B: 10%

[0109] TABLE II Total yarn Elongation at Modulus at 5% Ex. count (dtex) break (%) elongation (cN/tex)  1c 100 70 109 2 99 94.2 104 3 86 86.6 116 4 76.6 76.2 137

[0110] The yarns obtained at a speed of 4 200 m/min were drawn on a drawing block, and the properties of the yarns obtained are collated in Table III below. TABLE III Draw Yarn count Elongation at Modulus at 5% Ex. ratio (dtex) break (%) elongation (cN/tex)  1c 1.312 81.2 36.9 257 2 1.437 71.4 44.6 257

[0111] These tests show that it is possible to apply a higher draw ratio to the yarns in accordance with the invention while at the same time obtaining yarns with a 5% modulus that is identical to that obtained with a nylon-6,6 yarn with a higher residual elongation. This latter characteristic of high residual elongation makes it possible to improve the processability of the yarns.

EXAMPLE 5

[0112] The compounds are melt-blended using a twin-screw extrusion device and the melt is then spun, with a speed at the first point of call of 3 300 m/min, so as to obtain a continuous multifilament yarn of 55 dtex per 10 filaments. The temperature, pressure and spinning rate, and also the properties of the yarns obtained, are specified in Table IV.

COMPARATIVE EXAMPLE 6

[0113] A yarn is prepared as in Example 5, using compound C alone. The temperature, pressure and spinning rate, and also the properties of the yarns obtained, are specified in Table IV. TABLE IV Example 5 Comparative Example 6 Compound C 80% 100% Compound B 20% Spinning temperature 285° C. 320° C. Spinning rate Few breaks Very large number of breaks Pressure in the die 150 bar 150 bar Elongation at break (%) 95 95 Breaking stress (cN/tex) 25 25

Process for Manufacruting Yarns, Fibers and Filaments

[0114] The present invention relates to a process for manufacturing polyamide-based yarns, fibers and filaments, and also to the yarns, fibers and filaments that may be obtained by the process.

[0115] The present invention relates to a process for manufacturing yarns, fibers and filaments based on a polyamide composition having a molecular structure that makes it possible to improve the total production efficiency of the spinning process, especially by improving the drawability of the yarns produced, thus making it possible to have, for example, for an identical spinning speed, a much higher metreage of yarns per unit of time produced after spinning. The invention consists of a process for manufacturing synthetic, polyamide-based yarns, fibers and filaments, comprising the following operations:

[0116] i) Blending, in the melt, at least one of the compounds A and B below:

[0117] compound A: a linear polyamide

[0118] compound B chosen from the group comprising:

[0119] a polyamide or a polyamide composition comprising:

[0120] starburst or H-shaped macromolecular chains comprising one or more cores and at least three polyamide branches or three polyamide segments linked to the said core, obtained from amino acid and/or lactam monomers,

[0121] where appropriate, linear polyamide macromolecular chains obtained from amino acid and/or lactam monomers

[0122] the melt flow index of the polyamide or of the polyamide composition measured according to ISO standard 1133 at 275° C. under a 100 g charge being greater than 20 g/10 min, and

[0123] a multifunctional compound comprising at least three identical acid or amine functions,

[0124] ii) spinning the blend in the melt, and

[0125] iii) optionally drawing the said yarns, fibers or filaments obtained. 

1. Process for manufacturing synthetic, polyamide-based yarns, fibers and filaments, comprising the following operations: i) Blending, in the melt, at least one of the compounds A and B below: compound A: a linear polyamide compound B chosen from the group comprising: a polyamide or a polyamide composition comprising: starburst or H-shaped macromolecular chains comprising one or more cores and at least three polyamide branches or three polyamide segments linked to the said core, obtained from amino acid and/or lactam monomers, where appropriate, linear polyamide macromolecular chains obtained from amino acid and/or lactam monomers, the melt flow index of the polyamide or of the polyamide composition measured according to ISO standard 1133 at 275° C. under a 100 g charge being greater than 20 g/10 min, and a multifunctional compound comprising at least three identical acid or amine functions, ii) spinning the blend in the melt, and iii) optionally drawing the said yarn(s), fiber(s) or filament(s) obtained.
 2. Process according to claim 1, characterized in that the weight ratio between the starburst or H-shaped macromolecular chains and the sum of the starburst or H-shaped macromolecular chains and of the linear chains in compound B is between 0.1 and
 1. 3. Process according to either of the preceding claims, characterized in that compound B is a starburst polyamide obtained by copolymerization using a monomer blend comprising: a) a multifunctional compound comprising at least three reactive functions chosen from amines, carboxylic acids and derivatives thereof, the reactive functions being identical, b) monomers of general formulae (IIa) and/or (IIb) below: X—R₂—Y  (IIa) or

c) optionally, monomers of general formula (III) below: Z—R₃—Z  (III) in which: Z represents a function that is identical to that of the reactive functions of the multifunctional compound R₂ and R₃, which may be identical or different, represent substituted or unsubstituted, aliphatic, cycloaliphatic or aromatic hydrocarbon-based radicals containing from 2 to 20 carbon atoms, and possibly comprising hetero atoms, Y is a primary amine radical when X represents a carboxylic radical, or Y is a carboxylic radical when X represents a primary amine radical.
 4. Process according to either of claims 1 and 2, characterized in that compound B is an H-shaped polyamide obtained by copolymerization using a monomer blend comprising: a) 1 to 50 μmol per gram of polymer of compound B of a multifunctional compound comprising at least three reactive functions chosen from amines, carboxylic acids and derivatives thereof, the reactive functions being identical, b) lactams and/or amino acids c) a difunctional compound chosen from dicarboxylic acids and diamines, d) a multifunctional compound whose function is chosen from amines, carboxylic acids and derivatives thereof, the functions of c) and d) being amines when the functions of a) are acids, the functions of c) and d) being acids when the functions of a) are amines, the ratio in equivalents between the functional groups of a) and the sum of the functional groups of c) and d) being between 1.5 and 0.66, the ratio in equivalents between the functional groups of c) and the functional groups of d) being between 0.17 and 1.5.
 5. Process according to either of claims 1 and 2, characterized in that compound B is obtained by extruding a polyamide of the type obtained by polymerization of lactams and/or amino acids with a multifunctional compound comprising at least three reactive functions chosen from amines, carboxylic acids and derivatives thereof, the reactive functions being identical.
 6. Process according to one of claims 3 to 5, characterized in that the multifunctional compound has an arborescent or dendritic structure.
 7. Process according to one of claims 3 to 5, characterized in that the multifunctional compound is represented by formula (I) R1A—z]_(m)  (I) in which: R₁ is a linear or cyclic, aromatic or aliphatic hydrocarbon-based radical containing at least two carbon atoms and possibly comprising hetero atoms, A is a covalent bond or an aliphatic hydrocarbon-based radical containing from 1 to 6 carbon atoms, Z represents a primary amine radical or a carboxylic group, m is an integer between 3 and
 8. 8. Process according to claim 7, characterized in that the multifunctional compound is chosen from 2,2,6,6-tetra(P-carboxyethyl)cyclohexanone, trimesic acid, 2,4,6-tri(aminocaproic acid)-1,3,5-triazine and 4-aminoethyl-1,8-octanediamine.
 9. Process according to one of the preceding claims, characterized in that the weight proportion of compound B in the blend relative to the total weight of compounds A and B is less than 30%.
 10. Process according to claim 9, characterized in that the weight proportion of compound B in the blend relative to the total weight of compounds A and B is less than 20%.
 11. Process according to claim 10, characterized in that the weight proportion of compound B in the blend relative to the total weight of compounds A and B is less than 15%.
 12. Process according to one of the preceding claims, characterized in that the weight proportion of starburst or H-shaped macromolecular chains of compound B in the blend relative to the total weight of compounds A and B is less than 25%.
 13. Process according to one of the preceding claims, characterized in that the weight proportion of starburst or H-shaped macromolecular chains of compound B in the blend relative to the total weight of compounds A and B is less than 15%.
 14. Process according to one of the preceding claims, characterized in that compound A is a polyamide chosen from nylon-6, nylon-11, nylon-12 and blends and copolymers based on these polyamides.
 15. Process according to one of the preceding claims, characterized in that compound A is a nylon-6 with a relative viscosity of greater than 3.5.
 16. Process according to one of claims 1 to 13, characterized in that compound A is a linear polyamide obtained from diacid monomers and diamine monomers.
 17. Process according to claim 16, characterized in that compound A is a nylon-6,6 obtained from adipic acid and hexamethylenediamine.
 18. Process according to either of claims 16 and 17, characterized in that compound A is a copolyamide comprising at least 90 mol % of hexamethylenediamine adipate repeating units.
 19. Process according to one of the preceding claims, characterized in that a compound capable of catalysing the polycondensation of the polyamide is added to the blend, compounds A and B being in dried form.
 20. Process according to one of the preceding claims, characterized in that the spinning is performed with a spinning speed of greater than 3 500 m/min.
 21. Yarns, fibers and filaments that may be obtained by a process according to one of the preceding claims.
 22. Yarns, fibers and filaments that may be obtained by the process according to one of claims 1 to 20, characterized in that the monofilament yarn count is less than 0.8 dtex and preferably less than 0.6 dtex. 